This invention relates to the fabrication of three-dimensional objects using additive process modeling techniques. More particularly, the invention relates to forming three-dimensional objects by depositing a first solidifiable material in a predetermined pattern so as to form a three-dimensional object, in coordination with the depositing of a second solidifiable material so as to provide a support structure for the three-dimensional object as it is being built.
Additive process modeling machines make three-dimensional models by building up a modeling medium, based upon design data provided from a computer aided design (CAD) system. Three-dimensional models are used for functions including aesthetic judgments, proofing the mathematical CAD model, forming hard tooling, studying interference and space allocation, and testing functionality. One technique is to deposit solidifiable modeling material in a predetermined pattern, according to design data provided from a CAD system, with the build-up of multiple layers forming the model.
Examples of apparatus and methods for making three-dimensional models by depositing layers of solidifiable modeling material from an extrusion head are described in Valavaara U.S. Pat. No. 4,749,347; Crump U.S. Pat. No. 5,121,329; Batchelder, et al. U.S. Pat. No. 5,303,141; Crump U.S. Pat. No. 5,340,433; Batchelder, et al. U.S. Pat. No. 5,402,351; Crump, et al. U.S. Pat. No. 5,503,785; Batchelder, et al. U.S. Pat. No. 5,764,521; Danforth, et al. U.S. Pat. No. 5,900,207; Batchelder, et al. U.S. Pat. No. 5,968,561; Stuffle, et al. U.S. Pat. No. 6,067,480; and Batchelder et al. U.S. Pat. No. 6,238,613; all of which are assigned to Stratasys, Inc., the assignee of the present invention. The modeling material may be supplied to the extrusion head in solid form, for example in the form of a flexible filament wound on a supply reel or in the form of a solid rod, as disclosed in U.S. Pat. No. 5,121,329. As described in U.S. Pat. No. 4,749,347, modeling material may alternatively be pumped in liquid form from a reservoir. In any case, the extrusion head extrudes molten modeling material from a nozzle onto a base. The extruded material is deposited layer-by-layer in areas defined from the CAD model. A solidifiable material which adheres to the previous layer with an adequate bond upon solidification is used as the modeling material. Thermoplastic materials have been found particularly suitable for these deposition modeling techniques.
Another layered-deposition technique for building models from a solidifiable material deposits droplets of modeling material from nozzles of a jetting head. Examples of apparatus and methods for making three-dimensional models by depositing layers of solidifiable modeling material from a jetting head are described, for example, in U.S. Pat. No. 5,136,515 to Helinski et al., and U.S. Pat. No. 6,193,923 to Leyden et al.
In filament-fed Stratasys FDM® three-dimensional modeling machines of the current art, a filament strand of the modeling material (or support material) is advanced by a pair of motor-driven feed rollers into a liquifier carried by the extrusion head. Inside the liquifier, the filament is heated to a flowable temperature. The liquifier is pressurized by the “pumping” of the strand of filament into the liquifier by the feed rollers. The strand of filament itself acts as a piston, creating a pump. As the feed rollers continue to advance filament into the extrusion head, the force of the incoming filament strand extrudes the flowable material out from the dispensing nozzle where it is deposited onto a substrate removably mounted to a build platform. Stratasys FDM® three-dimensional modeling machines of the current art use as the modeling material acrylonitrile-butadiene-styrene (ABS) thermoplastic, a wax material, or polycarbonate.
In creating three-dimensional objects by additive process techniques, such as by depositing layers of solidifiable material, it is the rule rather than the exception that supporting layers or structures must be used underneath overhanging portions or in cavities of objects under construction, which are not directly supported by the modeling material itself. For example, if the object is a model of the interior of a subterranean cave and the cave prototype is constructed from the floor towards the ceiling, then a stalactite will require a temporary support until the ceiling is completed. Support layers or structure may be required for other reasons as well, such as allowing the model to be removed from a base, resisting a tendency for the model to deform while partially completed, and resisting forces applied to a partially completed model by the construction process.
A support structure may be built utilizing the same deposition techniques and apparatus by which the modeling material is deposited. The apparatus, under appropriate software control, produces additional geometry acting as a support structure for the overhanging or free-space segments of the object being formed. Support material is deposited either from a separate dispensing head within the modeling apparatus, or by the same dispensing head that deposits modeling material. The support material is chosen so that it removably adheres to the modeling material. Also, as the support material typically is used to create base layers of deposited material upon which the model is built, the support material should likewise removably adhere to the modeling substrate. Building support structures solves the problem of supporting the model, but creates the additional problem of removing the support structure from the finished model without causing damage to the model.
The problem of removing the support structure has been addressed by forming a weak, breakable bond between the model and the support structure, such as is described in U.S. Pat. No. 5,503,785. The '785 patent discloses a process by which a material that forms a weak, breakable bond with the modeling material is selected as either a support material or a release coating. Support material is deposited in layered fashion at the interface between the object and its support structure, or it is deposited in a layered fashion to form the support structure, in either case permitting the supports to be broken away after formation of the object. Support structures that must be broken apart from the object after it is built are known as “break-away” supports. Additionally, soluble support materials are known, which wash away in a bath. Stratasys, Inc. offers a material disclosed in pending U.S. patent application Ser. No. 10/019,160, sold under the name Waterworks™, for creating a soluble support structure.
Various styles of applying support material in layers are known. For example, the support material may be applied in short bead segments, termed “perforations”, where the support structure interfaces with the model under construction. The perforations reduce adhesion of the supports by limiting the area of contact with the model, aiding in the removal of breakaway supports. Also, layers of the support material may be interwoven with layers of the modeling material in building the support structure, a technique termed “composite supports”. The composite supports are weaker and therefore break apart more easily than homogenous supports. Another technique builds up support structures as an array of hollow rectangular pillars, having no side-by-side connection except that each is capped on the top by an interface layer or layers and capped on the bottom by a base layer or layers. This style, known as “box supports”, has the advantage of breaking off in sections once the base layer is removed, but has the disadvantage of a longer build time.
Apparatus and methods for building three-dimensional models by layered deposition of high-temperature engineering thermoplastics are disclosed in Swanson et al., U.S. patent application Ser. No. 09/804,401, filed on Feb. 27, 2001, and issued as U.S. Pat. No. 6,776,602 on Aug. 17, 2004 (herein “the '602 patent”); and Swanson et al., U.S. patent application Ser. No. 10/018,673, filed on Dec. 13, 2001, and issued as U.S. Pat. No. 6,722,872 on Apr. 20, 2004 (herein “the '872 patent”); which are assigned to Stratasys, Inc. These applications disclose the use of polycarbonate, polyetherimides, amorphous polyamides and sulfones for building three-dimensional models. Of these, only polycarbonate has been commercially implemented.
There is a continuing need to improve model strength and quality, by building models from high-performance engineering thermoplastics. Support structures for models made from such thermoplastics must withstand a high temperature environment and must be removable from the completed models.